1. Field of the Invention
This invention relates to impact printers and more particularly to a print hammer mechanism and print heed for use in moderate speed printers such as on the fly printers.
2. Description of the Prior Art
The rapid advances in the computer art have given rise to many types of moderate speed printing devices, i.e. printers which print from 500 to 1,000 lines per minute of information. Such equipment generally receives electrical output signals from the computer, and punches, prints or otherwise makes visible characters on a record medium to record the information processed by the computer. Generally such printers are of the back printing type wherein type characters on a type carrier (such as drum, chain, belt etc.) are moved past print positions behind a document on which printing is to be effected. In the impact printers, individual type hammers are provided generally for each column, and the type hammer is impelled to impact the record and a ribbon or other like instrument against the raised type characters on the type carrier to effect printing on the record medium.
The problem of rapidly providing high quality printout is related to many factors. In many applications there is a demand for multiple copies, with six or more copies being a typical requirement. In such applications the record medium is therefore a stacked form of sheets with carbon papers interleaved between the sheets. In the backtype printing printers, a multiple copy record medium is generally inserted into the printer, intermediate a print hammer array and a type carrier and ribbon. In any event, one of the problems associated with such printers is providing the requisite amount of impact energy to the print hammer means in order to legibly print at least six copies.
Another associated problem relates to the relationship between the impact hammer means and the type carrier. Where the type carrier is a relative stiff dense immovable carrier such as a print drum, a more massive hammer may be used since the type carrier does not resonate and does not provide as much dampening of the hammer motion. Where, however, the type carrier is a relatively flexible carrier, such as an endless flexible type band which resonates, the band after impact must return to its home position, something not required of a drum or wheel, which is a solid member. Since such endless bands commonly have a minute airspace behind the band, it is necessary to also move the band during the hammer contact time and thus the contact time with a band carrier typically tends to be greater than the contact time with a drum carrier, and excessive contact times result in reduced print quality. The longer that the print hammer mechanism is in contact with a moving type carrier, the more smear and other nondesirable print characteristics will be experienced. Such a phenomena presents a greater problem for the print head mechanism, since it can only be overcome by use of a hammer with lower mass. The dual problems of a low mass print hammer and a higher impact energy in turn both present problems to the design of the entire print head. One of the more acute problems presented is that with such a band type printer, the actuator device design becomes extremely critical, since far greater terminal velocities are required to get a print force out of a low mass hammer. As will be seen hereinafter, according to the novel print hammer we have provided, the aforementioned problem is solved by providing a low rotational inertia arm and uniform stress pring assembly to get an efficient transfer of energy from the actuator circuit into the moving hammer. By providing a low mass hammer and a low mass actuator arm with very high accelerations, the level of print quality is maintained. By way of example, the velocity of the print hammer, for one type of use which is made of one invention, is in excess of 200 inches per second.
Another problem associated with prior art impact printers relates to the normal maintenance required after the printer has been operated over a certain period of time. It is most desirable to keep the down time for maintenance as low as possible. With impact printers, one common form of maintenance relates to the print hammer array adjustments due to either failure of a part, wearing of parts of actuators, hammer, etc. or magnetic aging of parts. With prior art print hammers, the adjustments were made by gaining access through the rear of the printer, thereby requiring some disassembly and hence inconvenience. Hence, another of the object of this invention is to provide a print hammer assembly wherein adjustments or replacements can be done by gaining access to the print station from the front of the machine, eliminating disassembly.
It is yet another object of this invention to provide a print hammer and assembly therefor in which the hammer face is of double width, i.e. which the hammer face is sufficiently wide to occupy two columns of print locations, so that only one hammer and assembly therefor is provided for every other print column.
Prior art patents relating to impact hammers and assemblies therefor made of record in this application are U.S. Pat. Nos. 3,164,084; 3,188,947; 3,241,480 and 3,640,217.
The foregoing objects and other considerations are realized in one embodiment of an impact print head assembly in which an armature, base and side arms constitute an actuator for moving a hammer from a ready position toward the moving type carrier. Three leaf-type flexure springs are arranged with portions secured to the armature at one location and the base at another location so that a simple beam deflection is obtained and the energy imparted to the moving parts is absorbed uniformly by the spring assembly portion intermediate the two locations. In addition, the print hammers are inclined at a slight angle off a perpendicular in the plane of the hammer array to the print line, and each hammer has a double width face so that only one hammer and actuator assembly is required for every other column.